Limb-girdle muscular dystrophy type 2B is myogenic and of autosomal recessive inheritance. In 1998, it was reported
that LGMD2B was caused by mutations in the dysferin gene (DYSF) at chromosome 2p13, that is the responsible
gene for Miyoshi myopathy.
Deficiency of dysferlin causes attenuated sarcolemmal repair and results in muscle atrophy and weakness.
It has been reported that there are number of different types of limb-girdle muscular dystrophy (LGMD).
Autosomal dominant types are designated LGMD1, and autosomal recessive types are designated as LGMD2.
The subtypes of LGMD are named alphabetically in the order in which they are identified.
LGMD1 type locus geue LGMD1A 5q31 Myotilin LGMD1B lq11-q21 Lamin A/C LGMD1C 3p25 Caveolin-3 LGMD1D 7q36 DNAJB6 LGMD1E 6q23 ？ LGMD1F 7q32 ？ LGMD1G 4q21 ？
LGMD2 type locus geue LGMB2A
15q15.1 Calpain-3 LGMD2B 2p13 Dyaferlin LGMD2C 13q12 γ-sarcoglycan LGMD2D 17q12-q21.33 α-sarcoglycan LGMD2E 4q12 β-sarcoglycan LGMD2F 5q33 δ-sarcoglycan LGMD2G 17q12 Telethonin LGMD2H 9q31-q34 TRIM32 LGMD2 19q13.3 FKRP LGMD2J 2q31 Titin
The onset of LGMD2B is from one’s teens to early thirties, and proximal skeletal muscles begin to atrophy.
With the progression of the disease, distal skeletal muscles show atrophy similar to Miyoshi Myopathy.
The clinical difference between Miyoshi myopathy and LGMD2B remains unclear.
The Miyoshi myopathy with early-adult onset is characterized by
the primary involvement of distal muscles.
At an early stage, the patient cannot stand on their tiptoes or jump, tumbles down on a flat road while walking,
and has difficulty going up and down stairs.
Patients will be wheelchair-bound within 10 years from onset. Because the cardiac or respiratory system is not
affected in dysferlinopathy patients, the prognosis of dysferlinopathy is relatively better than other muscular diseases.
You may be diagnosed as one with a hepatic dysfunction because the value of creatine kinase (CK) in the serum is
10-folds higher than normal (5000-20000 IU/L) on clinical examination of blood.
This high CK value is a strong indication of muscular dystrophy.
In addition, you may have an electrocardiogram, lung capacity test, CT, MRI, electromyography, muscle biopsy and
bone density inspection. Histopathological examination of muscle will reveal dystrophic change (atrophy and
regeneration of myofiber, the increase of connective tissue), and immunohistochemical analysis using anti-dysferlin
antibody can definitively diagnose one with dysferlinopathy because dysferlin is deficient in the patient’s sarcolemma.
Muscle biopsy of the arm or leg will be performed once to confirm the diagnosis.
The responsible gene of LGMD2B is DYSF(the dysferlin gene), the same gene of Miyoshi myopathy.
Muscular disorder with mutations in the dysferlin gene is dysferlinopathy.
Muscular disease is a disorder involving muscle atrophy and is
classified as myogenic or neurogenic.
Myogenic muscular atrophy results from the problem of muscle itself and causes loss of muscle mass, while neurogenic
muscular atrophy is caused by the nerve problem.
CK (creatin kinase) is an enzyme in cardiac and muscle cells, and its normal
value is approximately 35-210.
Patients with muscular disease exhibit very high CK value, more than 10-times that of healthy individuals.
Healthy individuals show a high CK value after exercise, however it is much lower than a patients’ CK value.
The CK value indicates the degradation of skeletal muscle and varies in disease and/or the individual.
A child inheriting mutated genes froｍ parents will develop the disease, and a child inheriting a normal gene and
mutated gene will not develop the disease.
A single defective gene cause disease. In the case that parents are normal and patients, the inheritance probability
of the disease is 50%.
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